geographical accuracy (Graham Seaman)

[michael]

On Wed, 21 Feb 2007, Peter Corlett wrote:
> On Wed, Feb 21, 2007 at 12:20:31PM +0000, michael wrote:
>> Postcodes in central London are much much smaller than post codes in the
>> Scottish highlands. So, if the coordinates are derived form postcode data,
>> you would expect that the Scottish coordinates would but much less
>> accurate than the London ones...
>
> Well, a postcode covers multiple addresses, and you need the house number to
> uniquely identify a "delivery point" (or a letterbox as we normally call
> them).
>
> With a postcode only, a lookup is going to get you the co-ordinates of the
> first delivery point. Thus, from the point of the other delivery points,
> there is an error, but that's because it wasn't actually their address being
> looked up in the first place.
>

The OP was unsure of the source of the coordinate data, one possibility 
was that it was derived from postcode data.  If he looked at 10 remote 
rural locations and found them all accurate to 10 - 20 meters its unlikely 
that he has hit the postcode centroid every time

--
Michael
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Michael John Lush PhD			Tel:44-20-7679-5027
Nomenclature Bioinformatician		Fax:44-20-7387-3496
HUGO Gene Nomenclature Committee	Email:  nome at galton.ucl.ac.uk
The Galton Laboratory
University College London, UK
URL: http://www.gene.ucl.ac.uk/nomenclature/
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